Fluidized catalytic crackers, thermal crackers, and naphtha steam crackers are the main sources of olefins in a refinery. Significant commercial experience exists for cracking naphtha and heavier feeds to olefins, however limited technologies exist for dehydrogenating propane and butane.
The fluid catalytic cracking (FCC) process has become the pre-eminent source for motor gasoline in the USA and also serves the petrochemical industry with light olefins as petrochemical feedstock. Normal FCC operation cracks large molecules to a wide boiling mixture including olefins. The addition of ZSM-5 catalyst can further convert naphtha (gasoline) range olefins into butylenes, propylene and ethylene. Olefins exhibit a maximum yield as a function of ZSM-5 addition due to dilution of the normal FCC cracking catalyst and display a relatively fixed product distribution that favors propylene, with approximately 1.5 additional propylene per butylene.
The base FCC catalyst facilitates hydrogen transfer of olefins to their corresponding paraffin (e.g., isobutylene to isobutane). As main riser temperature is increased, olefin production also increases, but at high temperatures overcracking leads to significant hydrogen transfer and unwanted coke formation.
Butane feeds to steam crackers are typically used for the production of butene-1 and high purity butadiene. Steam crackers co-feed high concentrations of water to suppress coke formation on furnace tubes through reduced hydrocarbon partial pressure and gasification.
There remains a need for methods and systems that can convert light paraffins to gasoline boiling range hydrocarbons.